In general, the evolution of satellite system designs which allow for use of small, low cost earth stations has significantly increased the opportunity for an unauthorized, or "pirate" operator, to gain access to a communications satellite transponder. This is particularly true for conventional "bent pipe" pseudo-linear transponders.
More specifically, as shown in FIG. 1, a conventional bent pipe repeater 10 receives individual carriers transmitted by authorized earth stations via antenna system 12. The received signals are processed in a signal processing subsystem 13, wherein the carriers are amplified by a low noise amplifier 14 and then frequency translated, as a group, to the desired down link frequency via a mixer or translator 16. A local oscillator 18 is required for the frequency translation and is fixed in frequency and normally crystal controlled. The frequency translated spectrum is then demultiplexed in demux 20 into frequency passband channels. Each channel is applied to the appropriate channel conditioning circuits 22, and high power amplifiers 24. The outputs of the high power amplifiers are then recombined, using a frequency multiplexing technique in mux 26, and applied to the transmit antenna system 28 where they are radiated to the appropriate earth terminals. In such a conventional repeater, each carrier transmitted from the satellite is an exact amplified replica of the carrier received.
Past approaches to preventing unauthorized access to such repeaters have required inclusion of specialized on-board circuitry for demodulating, remodulating, signal processing, and signal switching. However, the addition of such on-board circuitry has not proven satisfactory because of a concomitant increase in system complexity and cost, as well as undesirably increasing payload size and weight of the satellite.